The invention relates generally to a delay circuit for delaying a signal within an integrated circuit, and more specifically to a temperature compensated delay path for a signal, the delay path based upon a temperature proximal to the integrated circuit.
A typical integrated circuit includes various components having numerous signals transmitted between components includes data signals, address signals, command signals, control signals, clock signals, read signals, write signals, and select signals. Depending on the application, signals are required to maintain synchronization to ensure proper operation. For example, in some environments, a signal is required to be present at a signal input port prior to a clock transition. Therefore, in one application, an input signal can be provided as an output signal at a clock transition. However, the signal must not arrive at the signal input port too early, such that the input signal will be transitioned as the output signal at a prior and undesired clock transition. Therefore, there is a window of time at which a signal must arrive at the signal input port.
Each signal within an integrated circuit travels from one component to another component via a signal path. Generally, the path of signals other than clock signals is relatively short. On the other hand, a clock signal path tends to be relatively long as it can span from a clock located at one end the integrated circuit to a component located at the other end of the integrated circuit. As a result, the time delay on the clock path tends to be longer than the time delay on other signal paths. Thus, time delays must be built into a signal path prior to the signal reaching the input port of a component so that the signal arrives at the input port in the desired timing window.
The two most recognized and used circuits for delaying a signal is a resister/capacitor (RC) element circuit and an inverter chain. An RC element circuit utilizes a reference source to load and unload an RC element, whose dimensions determine the required timing. A disadvantage to this implementation is the variation in time delay due to temperature dependency. The delay of an RC element circuit varies in different temperature environments.
An inverter chain is a simple serial circuit incorporating various pairs of inverters. Each pair of inverters first inverts the signal, and second inverts the inverted data signal, thereby providing an output signal equal in value to the input signal. However, each inverter introduces a time delay to the signal, thereby producing a time delayed signal. To introduce a minimal time delay, a minimal number of inverter pairs are provided along the signal path. Conversely, to introduce a longer time delay, several inverter pairs are provided along the signal path.
Inverters are commonly designed including complementary metal oxide semiconductors (CMOS) devices, which further include transistors. Transistors are the elements within the inverters that introduce the time delay. Generally, the speed of a transistor has a relatively high inversely proportional dependency on temperature changes within the transistor environment. The speed of the transistor decreases with an increase in the temperature of the transistor, and increases with a decrease in the temperature of the transistor. The temperature dependency factor of an inverter chain is especially critical in low power applications.
Integrated circuits are often subject to an extremely wide range of temperatures based upon specific applications. For example, depending on the application used, an integrated circuit may be subject to temperatures varying in range from −25° C. to 125° C. The time delay of an RC element circuit can be as great as 20% over the extended mobile application temperature range of −25° C. to 125° C. Likewise, the time delay of a simple single inverter pair can be as great as 20% over the extended mobile application temperature range of −25° C. to 125° C. The accumulated delay is even larger when delay components are connected serially.